I read below content from the Intel On-chip System Fabric (IOSF) spec. AS I understand, the IOSF is a technology for chip reuse and interconnect.
The sideband message interface covers most communication that is not
sent using inband transactions on the primary interface. Although IOSF
allows sending in-band message transactions on the primary
interface (such as interrupts and power management requests), some
implementations may choose to use the sideband message interface
instead.
I looked up the sideband, the explanation is from electric signal transmission context and seems not fit in.
So what does "side-band" and "in-band" mean in the quotation?
Best Answer
Many digital interfaces have more than one method of passing information. The main one is usually at high speed and takes the majority of the capability of the medium. Any information along this path is called "in-band".
However it is often necessary to communicate control or status information without disturbing the main data path - for example on HDMI there is the main video and sound transfer path but also a low speed I2C connection used to turn a TV or DvD player on or provide information on status- these are described as out-of band, or sometimes "side-band". This is completely different from the description you found that applies to modulation.
This out-of-band path may also be bi-directional even though the main data flow is unidirectional.